DESCRIPTION (provided by investigator): This is a renewal application to continue our work on the Sleep and Asthma Cohort (SAC) Study, HL079937, in which we started enrolling subjects in May 2006. Our overall goal is to elucidate the effects that asthma risk factors and sleep disordered breathing (SDB) have on sickle cell disease (SCD) morbidity and to better understand the biological basis progression of lung disease. In the SAC Study, we established a unique cohort of 251 children with SCD, who have received both pulmonary function testing (PFT) and full polysomnography (PSG), the largest cohort of children with SCD with this extensive evaluation in the world. Currently, the cohort has a mean prospective follow- up period of only 2.1 years, a time insufficient to assess the relationship between asthma risk factors on SCD-related morbidity (hospitalization for pain or ACS). At present, we do not know the relationship between asthma risk factors, SDB, and lung function abnormalities. We propose following the existing cohort for additional 4 years to assess these relationships with adequate statistical power. Further, our translational research efforts have focused on establishing a pre-clinical transgenic SCD mouse model of lung disease that strongly implicates fibrocytes, as a key component to pulmonary fibrosis and abnormal lung function. The project will have three inter-related Aims: 1) To determine if asthma risk factors (parental history of asthma and positive skin test for an aeroallergen) are associated with an increase incidence of pain and ACS episodes. Aim 2, to determine relationship between SDB and the presence of, or progression to, obstructive lung disease. Aim 3, to determine the longitudinal relationship between the percentage and phenotypes of circulating fibrocytes and evolution of abnormal lung function. Together, the results of this highly interactive collaboration of clinical and basic scientists will permit new insights into the natural history and pathogenesis of lung and sleep disease in SCD, providing a strong foundation for future targeted therapy.